It is already known that our moon was volcanically active billion of years ago, but new lunar samples that were brought to Earth from China’s Chang’e-5 mission have changed those estimates.
The moon is approximately 4.5 billion years old and during the first billion years, it was volcanically active. The activity was believed to have lasted for millions or even hundreds of millions of years. Based on the size of the moon, it was estimated that it began cooling down approximately 3 billion years ago, ultimately making the lunar surface rather quiet and uneventful. However, a lack of craters in certain areas of the lunar surface made scientists question whether there was something else going on that they didn’t know about. Lava flows would normally harden up into a smooth shape, meaning that volcanic activity may have lasted much longer than expected.
After conducting several different experiments, researchers came to the conclusion that the rocks of basalt that were collected from the moon (these are rocks that are created from volcanic activity) were indeed formed by lava flows that occurred 2 billion years ago.
But this raises more questions as chemical analysis didn’t provide the concentration of radioactive elements that should have been there if radioactive decay was the explanation for the volcanism. Perhaps there is another reason that kept the moon volcanically active for so long. One theory explores the possibility that Earth’s gravitational forces may have liquefied the interior of the moon, letting the magma flow for a much longer time as explained by Alexander Nemchin who is a planetary scientist at the Beijing SHRIMP Center and Curtin University in Bentley, Australia, “The moon was a lot closer 2 billion years ago.” When the moon started moving away from our planet, the forces would have become less powerful, therefore allowing the volcanic activity to decrease.
Another possibility is that constant bombardment of asteroids and comets may have kept the volcanic activity to continue; however, “at this point, any guess is a good guess,” said Jessica Barnes who is a planetary scientist at the University of Arizona in Tucson but wasn’t involved in the study.
For now, what we do know is that based on the lunar rocks that have been brought back to Earth and analyzed, there was volcanic activity on our moon as recently as just 2 billion years ago – much later than previously thought and by far the youngest moon rocks that have ever been collected. Interestingly, the rocks formed around the same time that multicellular life was first beginning to evolve on our planet.
The study was published in Science where it can be read in full.